This is a request for partial support of the Fourth International Workshop on Developmental Renal Physiology to be held in Montreal (Canada) on August 24-26 1989. The field of developmental renal physiology emerged some 40 years ago prompted by the finding that differences in renal function between infants and adults were not explained solely by differences in body size. It was, however, only in 1980 that those involved in the study of the maturing kidney had the opportunity to hold in New York the First International Workshop on Developmental Renal Physiology. The success of that meeting encouraged us to organize the subsequent workshops, the second held in Marburg (FRG) in 1983, and the third in Tokyo (Japan) in 1986. The programs of these meetings reflect the progress made in this field of research and the increased interest generated by the processes of growth and maturation among renal physiologists. The Fourth International Workshop on developmental Renal Physiology will be held at a time when renal physiologists, in an attempt to understand in greater depths various biologic processes, are becoming increasingly interested in their ontogeny. This tendency is reflected in the program which is heavily oriented towards cellular events and molecular biological methods. The meeting is scheduled for two and a half days. The mornings of the first two days will be dedicated to topics of major interest, namely renal growth and differentiation, and mechanisms of ion transport. the afternoons have been divided into two equal parts permitting us to schedule four subjects, namely renal metabolism, mineral transport, vasoactive substances, and neurotransmitters. Each session will be introduced by a state of the art presentation for which we have allowed 30 minutes. the presentations to follow are scheduled for 20 minutes, with the ensuing 10 minutes left for discussions. The last morning of the meeting will be divided into two parts, each accommodating two simultaneous symposia dedicated to new methods in kidney research. Poster presentations focusing on the method used rather than the topic to which it applies will provide the basis for discussion. As in the case of the main symposia, these seminars will emphasize molecular biology. The Workshop should provide not only an opportunity to review the progress made in the field of developmental renal physiology but it will also serve as a forum for exchange of ideas and as a vehicle for introducing new methods of investigation applicable to the maturing kidney.